The invention relates to a night vision module which is adaptable, as an input stage, on a daylight viewing and aiming device, for constituting a system which is operational at night by simply adding the module to the device.
Such a night vision module is of interest regarding ergonomy, since night viewing is through the same optical channel as daylight viewing. Furthermore, the degree of precision with which the night module is mechanically located on the daylight device is without effect on the harmonisation of the complete system, if the night module is itself harmonised (i.e. if its input axis is parallel to its optical output axis), all the more since the night module generally constitutes an afocal device having a magnification of 1.
Night viewing modules are already known of the type comprising an infra-red imaging unit and a unit for reproducing an image of the field of view of the imaging unit on a small size screen (typically the bottom of a cathode ray tube) for display in the input field of the daylight device.
In such a module, the image reproducing unit frequently has such a nature that it is subject, as time elapses or due to temperature variations, to a shift which results in a harmonisation error due to a displacement of the image of the field of view on the screen and possibly due to a change in the magnification. If practically the second cause of error is negligible, this is not so for the first one.